A liquid crystal display device utilizes optical anisotropy, dielectric anisotropy and so forth possessed by liquid crystal molecules in a liquid crystal composition. A classification based on an operating mode for the liquid crystal molecules includes a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a fringe field switching (FFS) mode and a vertical alignment (VA) mode.
A liquid crystal display device having a mode where a polymer and a liquid crystal composition are united are known. This is, for example, a polymer sustained alignment (PSA) mode or a polymer stabilized (PS) mode. In a liquid crystal display device having this mode, a liquid crystal composition to which a polymerizable compound is added is injected into a display device. A polymer is formed in the liquid crystal composition by the irradiation with ultraviolet light and by the polymerization of the polymerizable compound, while a voltage is applied between electrodes. According to this method, a liquid crystal display device is obtained in which the response time is decreased and the image burn-in is improved.
This method can be applied to a variety of operating modes of a liquid crystal display device, and modes such as PS-TN, PS-IPS, PS-FFS, PSA-VA and PSA-OCB are known. A polymerizable compound used for these kinds of modes seems to have a high ability to orient liquid crystal molecules. It is not said, however, that its solubility in a liquid crystal composition is high. An improvement of the solubility in a liquid crystal composition has been tried until now, and there is a tendency that as the solubility increases, the polymerization reactivity is decreased. Thus, the development of a polymerizable compound having a suitable balance between the solubility and the polymerization reactivity has been expected.